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Hembram KC, Chatterjee S, Sethy C, Nayak D, Pradhan R, Molla S, Bindhani BK, Kundu CN. Comparative and Mechanistic Study on the Anticancer Activity of Quinacrine-Based Silver and Gold Hybrid Nanoparticles in Head and Neck Cancer. Mol Pharm 2019; 16:3011-3023. [DOI: 10.1021/acs.molpharmaceut.9b00242] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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Al-Hazmi N, Alhazzazi T, Williams G, Stoeber K, Al-Dabbagh R. DNA replication licensing factor MCM2, geminin, and Ki67 define proliferative state and are linked with survival in oral squamous cell carcinoma. Eur J Oral Sci 2019; 126:186-196. [PMID: 29745471 DOI: 10.1111/eos.12420] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Oral squamous cell carcinoma (OSCC) is still an unabated global killer with little advancement in its survival rate. DNA replication licensing proteins and Aurora kinase A are biomarkers that play important roles in genomic stability. The expression profile of minichromosomal maintenance protein 2 (MCM2), Ki67, geminin, and Aurora-A were linked to clinicopathological and outcome parameters, survival, and DNA content in 125 cases of OSCC. Oral fibroepithelial polyps (OFEP) were controls. The OSCC tumour cells were in a rapidly proliferating state, as assessed by the increased expression profile of MCM2, Ki67, geminin, and Aurora-A and of the geminin/Ki67 ratio, and the decrease of the MCM2/Ki67 ratio, in OSCC compared with OFEP (P < 0.000). There was an association between expression of MCM2, Ki67, and geminin and tumour histologic and invasive front grade (P < 0.05). A total of 82% of the OSCC assessed had aneuploid DNA content, which was associated with increased expression intensity of Aurora-A (P = 0.01). Geminin and the geminin/Ki67 ratio were associated with TNM staging (P < 0.05), and weak expression of MCM2, Ki67, geminin, and Aurora-A were predictive of OSCC survival (P < 0.05). Dysregulation of the origin licensing pathway and the mitotic pathway are important events in OSCC, and the combined analysis of these proteins may contribute to improved treatment decisions.
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Affiliation(s)
- Nadia Al-Hazmi
- Department of Oral Biology, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia
| | - Turki Alhazzazi
- Department of Oral Biology, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia
| | - Gareth Williams
- Oncologica, London, UK.,Department of Pathology, UCL Cancer Institute, University College London, London, UK
| | - Kai Stoeber
- Department of Pathology, UCL Cancer Institute, University College London, London, UK
| | - Raghad Al-Dabbagh
- Department of Oral and Maxillofacial Prosthodontics, King Abdulaziz University, Jeddah, Saudi Arabia
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Abstract
Our knowledge of cell cycle regulatory mechanisms in apicomplexan parasites is very limited. In this study, we describe a novel Toxoplasma gondii factor that has a vital role in chromosome replication and the regulation of cytoplasmic and nuclear mitotic structures, and we named this factor ECR1 for essential for chromosome replication 1. ECR1 was discovered by complementation of a temperature-sensitive (ts) mutant that suffers lethal, uncontrolled chromosome replication at 40°C similar to a ts mutant carrying a defect in topoisomerase. ECR1 is a 52-kDa protein containing divergent RING and TRAF-Sina-like zinc binding domains that are dynamically expressed in the tachyzoite cell cycle. ECR1 first appears in the unique spindle compartment of the Apicomplexa (centrocone) of the nuclear envelope in early S phase and then in the nucleus in late S phase where it reaches maximum expression. Following nuclear division, but before daughter parasites separate from the mother parasite, ECR1 is downregulated and is absent in new daughter parasites. The proteomics of ECR1 identified interactions with the ubiquitin-mediated protein degradation machinery and the minichromosome maintenance complex, and the loss of ECR1 led to increased stability of a key member of this complex, MCM2. ECR1 also forms a stable complex with the cyclin-dependent kinase (CDK)-related kinase, Tgondii Crk5 (TgCrk5), which displays a similar cell cycle expression and localization during tachyzoite replication. Importantly, the localization of ECR1/TgCrk5 in the centrocone indicates that this Apicomplexa-specific spindle compartment houses important regulatory factors that control the parasite cell cycle.IMPORTANCE Parasites of the apicomplexan family are important causes of human disease, including malaria, toxoplasmosis, and cryptosporidiosis. Parasite growth is the underlying cause of pathogenesis, yet despite this importance, the molecular basis for parasite replication is poorly understood. Filling this knowledge gap cannot be accomplished by mining recent whole-genome sequencing data because apicomplexan cell cycles differ substantially and lack many of the key regulatory factors of well-studied yeast and mammalian cell division models. We have utilized forward genetics to discover essential factors that regulate cell division in these parasites using the Toxoplasma gondii model. An example of this approach is described here with the discovery of a putative E3 ligase/protein kinase mechanism involved in regulating chromosome replication and mitotic processes of asexual stage parasites.
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Gillespie PJ, Neusiedler J, Creavin K, Chadha GS, Blow JJ. Cell Cycle Synchronization in Xenopus Egg Extracts. Methods Mol Biol 2016; 1342:101-47. [PMID: 26254920 DOI: 10.1007/978-1-4939-2957-3_6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Many important discoveries in cell cycle research have been made using cell-free extracts prepared from the eggs of the South African clawed frog Xenopus laevis. These extracts efficiently support the key nuclear functions of the eukaryotic cell cycle in vitro under apparently the same controls that exist in vivo. The Xenopus cell-free system is therefore uniquely suited to the study of the mechanisms, dynamics and integration of cell cycle regulated processes at a biochemical level. Here, we describe methods currently in use in our laboratory for the preparation of Xenopus egg extracts and demembranated sperm nuclei. We detail how these extracts can be used to study the key transitions of the eukaryotic cell cycle and describe conditions under which these transitions can be manipulated by addition of drugs that either retard or advance passage. In addition, we describe in detail essential techniques that provide a practical starting point for investigating the function of proteins involved in the operation of the eukaryotic cell cycle.
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Affiliation(s)
- Peter J Gillespie
- Centre for Gene Regulation & Expression, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
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Kamenz J, Mihaljev T, Kubis A, Legewie S, Hauf S. Robust Ordering of Anaphase Events by Adaptive Thresholds and Competing Degradation Pathways. Mol Cell 2015; 60:446-59. [PMID: 26527280 DOI: 10.1016/j.molcel.2015.09.022] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2015] [Revised: 08/08/2015] [Accepted: 09/24/2015] [Indexed: 11/26/2022]
Abstract
The splitting of chromosomes in anaphase and their delivery into the daughter cells needs to be accurately executed to maintain genome stability. Chromosome splitting requires the degradation of securin, whereas the distribution of the chromosomes into the daughter cells requires the degradation of cyclin B. We show that cells encounter and tolerate variations in the abundance of securin or cyclin B. This makes the concurrent onset of securin and cyclin B degradation insufficient to guarantee that early anaphase events occur in the correct order. We uncover that the timing of chromosome splitting is not determined by reaching a fixed securin level, but that this level adapts to the securin degradation kinetics. In conjunction with securin and cyclin B competing for degradation during anaphase, this provides robustness to the temporal order of anaphase events. Our work reveals how parallel cell-cycle pathways can be temporally coordinated despite variability in protein concentrations.
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Affiliation(s)
- Julia Kamenz
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA; Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA 24061, USA; Friedrich Miescher Laboratory of the Max Planck Society, 72076 Tuebingen, Germany
| | | | - Armin Kubis
- Friedrich Miescher Laboratory of the Max Planck Society, 72076 Tuebingen, Germany
| | - Stefan Legewie
- Institute of Molecular Biology (IMB), 55128 Mainz, Germany.
| | - Silke Hauf
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA; Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA 24061, USA; Friedrich Miescher Laboratory of the Max Planck Society, 72076 Tuebingen, Germany.
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Zhang Y, Jiang Z, Li L, Zhou Y, Song Z, Shu M. Geminin interference facilitates vascular smooth muscle cell proliferation by upregulation of CDK-1. Cardiovasc Drugs Ther 2015; 28:407-14. [PMID: 25189787 DOI: 10.1007/s10557-014-6550-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
PURPOSE Geminin has been correlated with vascular smooth muscle cell (VSMC) proliferation, but its mechanism is unclear. We selectively silenced the geminin gene of rat VSMCs by using RNAi technology and examined how geminin regulated VSMC proliferation. METHODS By using RNA interference in A10 cells and flow cytometry, (3)H-thymidine and 5-ethynyl-2'-deoxyuridine (EdU) measurements were used to detect VSMC proliferation. We performed a Western blot, polymerase chain reaction, and immunohistochemistry to detect the expression and location of geminin and cyclin-dependent kinase-1 (CDK1) in VSMCs. RESULTS Silencing geminin significantly increased (3)H-thymidine and EdU incorporation in VSMCs. We observed a significant increase in (3)H-thymidine incorporation 24 h after a serum challenge in the geminin-RNAi-lentiviral vector group (4401.38 ± 438.39 cpm/mg), versus the non-targeting geminin-lentiviral vector (2836.88 ± 476.18 cpm/mg) and control groups (3069.50 ± 508.18 cpm/mg; P < 0.05). In the geminin-RNAi-lentiviral vector group, the EdU-positive cell rate was significantly increased (0.75 ± 0.03; P < 0.05), versus the non-targeting geminin-lentiviral vector (0.41 ± 0.0) or control group (0.40 ± 0.03). Geminin promoted VSMC proliferation, accelerating G0/G1-S cell-cycle progression (G0/G1 cells, 10 % decrease; S-phase cells, approximate 6 % increase) 12 h after serum withdrawal. Both CDK1 protein and mRNA expression were significantly increased in the positive group versus the controls. The immunofluorescence and co-immunoprecipitation results revealed a close interaction existed between CDK1 and the geminin gene in VSMC proliferation. CONCLUSIONS Geminin gene inhibition could augment VSMC proliferation by increasing CDK1 expression; thus, geminin may be a potential target for treating vascular diseases, specifically VSMCs.
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Affiliation(s)
- Yuanyuan Zhang
- Department of Cardiology, Southwest Hospital, Third Military Medical University, Gaotanyan St, Shapingba District, Chongqing, 400038, People's Republic of China
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Musiałek MW, Rybaczek D. Behavior of replication origins in Eukaryota - spatio-temporal dynamics of licensing and firing. Cell Cycle 2015; 14:2251-64. [PMID: 26030591 DOI: 10.1080/15384101.2015.1056421] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Although every organism shares some common features of replication, this process varies greatly among eukaryotic species. Current data show that mathematical models of the organization of origins based on possibility theory may be applied (and remain accurate) in every model organism i.e. from yeast to humans. The major differences lie within the dynamics of origin firing and the regulation mechanisms that have evolved to meet new challenges throughout the evolution of the organism. This article elaborates on the relations between chromatin structure, organization of origins, their firing times and the impact that these features can have on genome stability, showing both differences and parallels inside the eukaryotic domain.
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Key Words
- APC, anaphase promoting complex
- ARS, autonomously replicating sequences
- ATR, ataxia telangiectasia mutated and Rad3-related kinase
- C-Frag, chromosome fragmentation
- CDK, cyclin-dependent kinase
- CDT, C-terminus domain
- CEN, centromere
- CFSs, chromosome fragile sites
- CIN, chromosome instability
- CMG, Cdc45-MCM-GINS complex
- Cdc45, cell division control protein 45
- Cdc6, cell division control protein 6
- Cdt1, chromatin licensing and DNA replication factor 1
- Chk1, checkpoint kinase 1
- Clb2, G2/mitotic-specific cyclin Clb2
- DCR, Ddb1-Cu14a-Roc1 complex
- DDK, Dbf-4-dependent kinase
- DSBs, double strand breaks
- Dbf4, protein Dbf4 homolog A
- Dfp1, Hsk1-Dfp1 kinase complex regulatory subunit Dfp1
- Dpb11, DNA replication regulator Dpb11
- E2F, E2F transcription factor
- EL, early to late origins transition
- ETG1, E2F target gene 1/replisome factor
- Fkh, fork head domain protein
- GCN5, histone acetyltransferase GCN5
- GINS, go-ichi-ni-san
- LE, late to early origins transition
- MCM2–7, minichromosome maintenance helicase complex
- NDT, N-terminus domain
- ORC, origin recognition complex
- ORCA, origin recognition complex subunit A
- PCC, premature chromosome condensation
- PCNA, proliferating cell nuclear antigen
- RO, replication origin
- RPD3, histone deacetylase 3
- RTC, replication timing control
- Rif1, replication timing regulatory factor 1
- SCF, Skp1-Cullin-F-Box ligase
- SIR, sulfite reductase
- Sld2, replication regulator Sld2
- Sld3, replication regulator Sld3
- Swi6, chromatin-associated protein swi6
- Taz1, telomere length regulator taz1
- YKU70, yeast Ku protein.
- dormant origins
- mathematical models of replication
- ori, origin
- origin competence
- origin efficiency
- origin firing
- origin licensing
- p53, tumor suppressor protein p53
- replication timing
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Affiliation(s)
- Marcelina W Musiałek
- a Department of Cytophysiology ; Institute of Experimental Biology; Faculty of Biology and Environmental Protection; University of Łódź ; Łódź , Poland
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Aurora-A controls pre-replicative complex assembly and DNA replication by stabilizing geminin in mitosis. Nat Commun 2013; 4:1885. [PMID: 23695679 PMCID: PMC3675325 DOI: 10.1038/ncomms2859] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Accepted: 04/10/2013] [Indexed: 01/14/2023] Open
Abstract
Geminin, an essential factor for DNA replication, directly binds to the licensing factor Cdt1 and inhibits pre-replicative complex formation to prevent re-replication. In G1, geminin levels are controlled by the anaphase-promoting complex/cyclosome (APC/C) ubiquitin ligase complex, which targets geminin for proteasomal degradation to allow pre-replicative complex formation. Conversely, from S to G2, geminin is stabilized due to APC/C ubiquitin ligase complex inhibition, ensuring the inhibition of pre-replicative complex formation. However, mitotic regulation of geminin has hitherto not been described. Here we show that Aurora-A phosphorylates geminin on Thr25 during M phase, and this event induces geminin stabilization by preventing its APC/C ubiquitin ligase complex-mediated degradation during mitosis. In turn, stabilized geminin inhibits SCFSkp2-mediated degradation of Cdt1 to ensure pre-replicative complex formation in the ensuing S phase. The Aurora-A–geminin–Cdt1 axis therefore represents a critical regulator of proper DNA replication. Geminin blocks the inappropriate assembly of pre-replication complexes on DNA, and this activity is inhibited in G1 by its proteasomal degradation. Tsunematsu et al. demonstrate that geminin is stabilized during mitosis due to its phosphorylation by the mitotic kinase Aurora-A.
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Neelsen KJ, Zanini IM, Mijic S, Herrador R, Zellweger R, Ray Chaudhuri A, Creavin KD, Blow JJ, Lopes M. Deregulated origin licensing leads to chromosomal breaks by rereplication of a gapped DNA template. Genes Dev 2013; 27:2537-42. [PMID: 24298053 PMCID: PMC3861667 DOI: 10.1101/gad.226373.113] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Accepted: 10/30/2013] [Indexed: 01/01/2023]
Abstract
Deregulated origin licensing and rereplication promote genome instability and tumorigenesis by largely elusive mechanisms. Investigating the consequences of Early mitotic inhibitor 1 (Emi1) depletion in human cells, previously associated with rereplication, we show by DNA fiber labeling that origin reactivation occurs rapidly, well before accumulation of cells with >4N DNA, and is associated with checkpoint-blind ssDNA gaps and replication fork reversal. Massive RPA chromatin loading, formation of small chromosomal fragments, and checkpoint activation occur only later, once cells complete bulk DNA replication. We propose that deregulated origin firing leads to undetected discontinuities on newly replicated DNA, which ultimately cause breakage of rereplicating forks.
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Affiliation(s)
- Kai J. Neelsen
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Isabella M.Y. Zanini
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Sofija Mijic
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Raquel Herrador
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Ralph Zellweger
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Arnab Ray Chaudhuri
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Kevin D. Creavin
- Centre for Gene Regulation and Expression, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - J. Julian Blow
- Centre for Gene Regulation and Expression, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Massimo Lopes
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
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Ganoth A, Tsfadia Y, Wiener R. Ubiquitin: Molecular modeling and simulations. J Mol Graph Model 2013; 46:29-40. [DOI: 10.1016/j.jmgm.2013.09.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 09/09/2013] [Accepted: 09/10/2013] [Indexed: 01/18/2023]
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Dimaki M, Xouri G, Symeonidou IE, Sirinian C, Nishitani H, Taraviras S, Lygerou Z. Cell cycle-dependent subcellular translocation of the human DNA licensing inhibitor geminin. J Biol Chem 2013; 288:23953-63. [PMID: 23814078 DOI: 10.1074/jbc.m113.453092] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Once per cell cycle replication is crucial for maintaining genome integrity. Geminin interacts with the licensing factor Cdt1 to prevent untimely replication and is controlled by APC/C-dependent cell cycle specific proteolysis during mitosis and in G1. We show here that human geminin, when expressed in human cells in culture under a constitutive promoter, is excluded from the nucleus during part of the G1 phase and at the transition from G0 to G1. The N-terminal 30 amino acids of geminin, which contain its destruction box, are essential for nuclear exclusion. In addition, 30 amino acids within the central domain of geminin are required for both nuclear exclusion and nuclear accumulation. Cdt1 overexpression targets geminin to the nucleus, while reducing Cdt1 levels by RNAi leads to the appearance of endogenous geminin in the cytoplasm. Our data propose a novel means of regulating the balance of Cdt1/geminin in human cells, at the level of the subcellular localization of geminin.
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Affiliation(s)
- Maria Dimaki
- Laboratory of General Biology, School of Medicine, University of Patras, 26500 Rio, Patras, Greece
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12
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Clijsters L, Ogink J, Wolthuis R. The spindle checkpoint, APC/C(Cdc20), and APC/C(Cdh1) play distinct roles in connecting mitosis to S phase. ACTA ACUST UNITED AC 2013; 201:1013-26. [PMID: 23775192 PMCID: PMC3691463 DOI: 10.1083/jcb.201211019] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The spindle checkpoint, APC/C-Cdc20, and APC/C-Cdh1 act successively to connect disappearance of geminin and cyclin B1 to a peak of Cdt1 and Cdc6. DNA replication depends on a preceding licensing event by Cdt1 and Cdc6. In animal cells, relicensing after S phase but before mitosis is prevented by the Cdt1 inhibitor geminin and mitotic cyclin activity. Here, we show that geminin, like cyclin B1 and securin, is a bona fide target of the spindle checkpoint and APC/CCdc20. Cyclin B1 and geminin are degraded simultaneously during metaphase, which directs Cdt1 accumulation on segregating sister chromatids. Subsequent activation of APC/CCdh1 leads to degradation of Cdc6 well before Cdt1 becomes unstable in a replication-coupled manner. In mitosis, the spindle checkpoint supports Cdt1 accumulation, which promotes S phase onset. We conclude that the spindle checkpoint, APC/CCdc20, and APC/CCdh1 act successively to ensure that the disappearance of licensing inhibitors coincides exactly with a peak of Cdt1 and Cdc6. Whereas cell cycle entry from quiescence requires Cdc6 resynthesis, our results indicate that proliferating cells use a window of time in mitosis, before Cdc6 is degraded, as an earlier opportunity to direct S phase.
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Affiliation(s)
- Linda Clijsters
- Division of Cell Biology I (B5), The Netherlands Cancer Institute (NKI-AvL), 1066 CX Amsterdam, Netherlands.
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13
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Gillespie PJ, Gambus A, Blow JJ. Preparation and use of Xenopus egg extracts to study DNA replication and chromatin associated proteins. Methods 2012; 57:203-13. [PMID: 22521908 PMCID: PMC3437562 DOI: 10.1016/j.ymeth.2012.03.029] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2011] [Revised: 03/23/2012] [Accepted: 03/24/2012] [Indexed: 12/20/2022] Open
Abstract
The use of cell-free extracts prepared from eggs of the South African clawed toad, Xenopus laevis, has led to many important discoveries in cell cycle research. These egg extracts recapitulate the key nuclear transitions of the eukaryotic cell cycle in vitro under apparently the same controls that exist in vivo. DNA added to the extract is first assembled into a nucleus and is then efficiently replicated. Progression of the extract into mitosis then allows the separation of paired sister chromatids. The Xenopus cell-free system is therefore uniquely suited to the study of the mechanisms, dynamics and integration of cell cycle regulated processes at a biochemical level. In this article we describe methods currently in use in our laboratory for the preparation of Xenopus egg extracts and demembranated sperm nuclei for the study of DNA replication in vitro. We also detail how DNA replication can be quantified in this system. In addition, we describe methods for isolating chromatin and chromatin-bound protein complexes from egg extracts. These recently developed and revised techniques provide a practical starting point for investigating the function of proteins involved in DNA replication.
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Affiliation(s)
- Peter J. Gillespie
- Wellcome Trust Centre for Gene Regulation & Expression, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Agnieszka Gambus
- School of Cancer Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - J. Julian Blow
- Wellcome Trust Centre for Gene Regulation & Expression, University of Dundee, Dow Street, Dundee DD1 5EH, UK
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14
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Dynamic association of ORCA with prereplicative complex components regulates DNA replication initiation. Mol Cell Biol 2012; 32:3107-20. [PMID: 22645314 DOI: 10.1128/mcb.00362-12] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
In eukaryotes, initiation of DNA replication requires the assembly of a multiprotein prereplicative complex (pre-RC) at the origins. We recently reported that a WD repeat-containing protein, origin recognition complex (ORC)-associated (ORCA/LRWD1), plays a crucial role in stabilizing ORC to chromatin. Here, we find that ORCA is required for the G(1)-to-S-phase transition in human cells. In addition to binding to ORC, ORCA associates with Cdt1 and its inhibitor, geminin. Single-molecule pulldown experiments demonstrate that each molecule of ORCA can bind to one molecule of ORC, one molecule of Cdt1, and two molecules of geminin. Further, ORCA directly interacts with the N terminus of Orc2, and the stability of ORCA is dependent on its association with Orc2. ORCA associates with Orc2 throughout the cell cycle, with Cdt1 during mitosis and G(1), and with geminin in post-G(1) cells. Overexpression of geminin results in the loss of interaction between ORCA and Cdt1, suggesting that increased levels of geminin in post-G(1) cells titrate Cdt1 away from ORCA. We propose that the dynamic association of ORCA with pre-RC components modulates the assembly of its interacting partners on chromatin and facilitates DNA replication initiation.
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15
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Klotz-Noack K, McIntosh D, Schurch N, Pratt N, Blow JJ. Re-replication induced by geminin depletion occurs from G2 and is enhanced by checkpoint activation. J Cell Sci 2012; 125:2436-45. [PMID: 22366459 PMCID: PMC3481538 DOI: 10.1242/jcs.100883] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To prevent re-replication of DNA in a single cell cycle, the licensing of replication origins by Mcm2-7 is prevented during S and G2 phases. Animal cells achieve this by cell-cycle-regulated proteolysis of the essential licensing factor Cdt1 and inhibition of Cdt1 by geminin. Here we investigate the consequences of ablating geminin in synchronised human U2OS cells. Following geminin loss, cells complete an apparently normal S phase, but a proportion arrest at the G2-M boundary. When Cdt1 accumulates in these cells, DNA re-replicates, suggesting that the key role of geminin is to prevent re-licensing in G2. If cell cycle checkpoints are inhibited in cells lacking geminin, cells progress through mitosis and less re-replication occurs. Checkpoint kinases thereby amplify re-replication into an all-or-nothing response by delaying geminin-depleted cells in G2. Deep DNA sequencing revealed no preferential re-replication of specific genomic regions after geminin depletion. This is consistent with the observation that cells in G2 have lost their replication timing information. By contrast, when Cdt1 is overexpressed or is stabilised by the neddylation inhibitor MLN4924, re-replication can occur throughout S phase.
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Affiliation(s)
- Kathleen Klotz-Noack
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Debbie McIntosh
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Nicholas Schurch
- Data Analysis Group, College of Life Sciences, University of Dundee DD1 5EH, UK
| | - Norman Pratt
- Department of Human Genetics, Ninewells Hospital, Dundee DD1 9SY, UK
| | - J. Julian Blow
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
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Yang VS, Carter SA, Ng Y, Hyland SJ, Tachibana-Konwalski K, Fisher RA, Sebire NJ, Seckl MJ, Pedersen RA, Laskey RA, Gonzalez MA. Distinct activities of the anaphase-promoting complex/cyclosome (APC/C) in mouse embryonic cells. Cell Cycle 2012; 11:846-55. [PMID: 22333576 DOI: 10.4161/cc.11.5.19251] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The first differentiation event in mammalian development gives rise to the blastocyst, consisting of two cell lineages that have also segregated in how the cell cycle is structured. Pluripotent cells of the inner cell mass divide mitotically to retain a diploid DNA content, but the outer trophoblast cells can amplify their genomes more than 500-fold by undergoing multiple rounds of DNA replication, completely bypassing mitosis. Central to this striking divergence in cell cycle control is the E3 ubiquitin-ligase activity of the anaphase-promoting complex or cyclosome (APC/C). Extended suppression of APC/C activity during interphase of mouse pluripotent cells promotes rapid cell cycle progression by allowing stabilization of cyclins, whereas unopposed APC/C activity during S phase of mouse trophoblast cells triggers proteasomal-mediated degradation of geminin and giant cell formation. While differential APC/C activity might govern the atypical cell cycles observed in pre-implantation mouse embryos, geminin is a critical APC/C substrate that: (1) escapes degradation in pluripotent cells to maintain expression of Oct4, Sox2 and Nanog; and (2) mediates specification and endoreduplication when targeted for ectopic destruction in trophoblast. Thus, in contrast to trophoblast giant cells that lack geminin, geminin is preserved in both mouse pluripotent cells and non-endoreduplicating human cytotrophoblast cells.
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Affiliation(s)
- Valerie S Yang
- MRC Cancer Cell Unit, Hutchison-MRC Research Centre, Cambridge, UK
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17
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Sonneville R, Querenet M, Craig A, Gartner A, Blow JJ. The dynamics of replication licensing in live Caenorhabditis elegans embryos. J Cell Biol 2012; 196:233-46. [PMID: 22249291 PMCID: PMC3265957 DOI: 10.1083/jcb.201110080] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2011] [Accepted: 12/13/2011] [Indexed: 01/07/2023] Open
Abstract
Accurate DNA replication requires proper regulation of replication licensing, which entails loading MCM-2-7 onto replication origins. In this paper, we provide the first comprehensive view of replication licensing in vivo, using video microscopy of Caenorhabditis elegans embryos. As expected, MCM-2-7 loading in late M phase depended on the prereplicative complex (pre-RC) proteins: origin recognition complex (ORC), CDC-6, and CDT-1. However, many features we observed have not been described before: GFP-ORC-1 bound chromatin independently of ORC-2-5, and CDC-6 bound chromatin independently of ORC, whereas CDT-1 and MCM-2-7 DNA binding was interdependent. MCM-3 chromatin loading was irreversible, but CDC-6 and ORC turned over rapidly, consistent with ORC/CDC-6 loading multiple MCM-2-7 complexes. MCM-2-7 chromatin loading further reduced ORC and CDC-6 DNA binding. This dynamic behavior creates a feedback loop allowing ORC/CDC-6 to repeatedly load MCM-2-7 and distribute licensed origins along chromosomal DNA. During S phase, ORC and CDC-6 were excluded from nuclei, and DNA was overreplicated in export-defective cells. Thus, nucleocytoplasmic compartmentalization of licensing factors ensures that DNA replication occurs only once.
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Affiliation(s)
- Remi Sonneville
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
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18
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Kisielewska J, Blow JJ. Dynamic interactions of high Cdt1 and geminin levels regulate S phase in early Xenopus embryos. Development 2012; 139:63-74. [PMID: 22096080 PMCID: PMC3492748 DOI: 10.1242/dev.068676] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cdt1 plays a key role in licensing DNA for replication. In the somatic cells of metazoans, both Cdt1 and its natural inhibitor geminin show reciprocal fluctuations in their protein levels owing to cell cycle-dependent proteolysis. Here, we show that the protein levels of Cdt1 and geminin are persistently high during the rapid cell cycles of the early Xenopus embryo. Immunoprecipitation of Cdt1 and geminin complexes, together with their cell cycle spatiotemporal dynamics, strongly supports the hypothesis that Cdt1 licensing activity is regulated by periodic interaction with geminin rather than its proteolysis. Overexpression of ectopic geminin slows down, but neither arrests early embryonic cell cycles nor affects endogenous geminin levels; apparent embryonic lethality is observed around 3-4 hours after mid-blastula transition. However, functional knockdown of geminin by ΔCdt1_193-447, which lacks licensing activity and degradation sequences, causes cell cycle arrest and DNA damage in affected cells. This contributes to subsequent developmental defects in treated embryos. Our results clearly show that rapidly proliferating early Xenopus embryonic cells are able to regulate replication licensing in the persistent presence of high levels of licensing proteins by relying on changing interactions between Cdt1 and geminin during the cell cycle, but not their degradation.
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Affiliation(s)
- Jolanta Kisielewska
- University of Newcastle, The Institute for Cell and Molecular Biosciences, Framlington Place, NE2 4HH, Newcastle-Upon-Tyne, UK.
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19
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Ode KL, Fujimoto K, Kubota Y, Takisawa H. Inter-origin cooperativity of geminin action establishes an all-or-none switch for replication origin licensing. Genes Cells 2011; 16:380-96. [PMID: 21426446 DOI: 10.1111/j.1365-2443.2011.01501.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In metazoans, geminin functions as a molecular switch for preventing re-replication of chromosomal DNA. Geminin binds to and inhibits Cdt1, which is required for replication origin licensing, but little is known about the mechanisms underlying geminin's all-or-none action in licensing inhibition. Using Xenopus egg extract, we found that the all-or-none activity correlated with the formation of Cdt1 foci on chromatin, suggesting that multiple Cdt1-geminin complexes on origins cooperatively inhibit licensing. Based on experimental identification of licensing intermediates targeted by geminin and Cdt1, we developed a mathematical model of the licensing process. The model involves positive feedback owing to the cooperative action of geminin at neighboring origins and accurately accounts for the licensing activity mediated by geminin and Cdt1 in the extracts. The model also predicts that such cooperativity leads to clustering of licensing-inhibited origins, an idea that is supported by the experimentally measured distribution of inter-origin distances. We propose that geminin inhibits licensing through an inter-origin interaction, ensuring strict and coordinated control of multiple replication origins on chromosomes.
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Affiliation(s)
- Koji L Ode
- Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
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20
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Aze A, Fayet C, Lapasset L, Genevière A. Replication origins are already licensed in G1 arrested unfertilized sea urchin eggs. Dev Biol 2010; 340:557-70. [DOI: 10.1016/j.ydbio.2010.02.009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2009] [Revised: 02/02/2010] [Accepted: 02/04/2010] [Indexed: 11/24/2022]
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21
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Li C, Jin J. DNA replication licensing control and rereplication prevention. Protein Cell 2010; 1:227-36. [PMID: 21203969 DOI: 10.1007/s13238-010-0032-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2010] [Accepted: 01/18/2010] [Indexed: 01/23/2023] Open
Abstract
Eukaryotic DNA replication is tightly restricted to only once per cell cycle in order to maintain genome stability. Cells use multiple mechanisms to control the assembly of the prereplication complex (pre-RC), a process known as replication licensing. This review focuses on the regulation of replication licensing by posttranslational modifications of the licensing factors, including phosphorylation, ubiquitylation and acetylation. These modifications are critical in establishing the pre-RC complexes as well as preventing rereplication in each cell cycle. The relationship between rereplication and diseases, including cancer and virus infection, is discussed as well.
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Affiliation(s)
- Chonghua Li
- Department of Biochemistry and Molecular Biology, The University of Texas Medical School at Houston, Houston, TX 77030, USA
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22
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Khayrutdinov BI, Bae WJ, Yun YM, Lee JH, Tsuyama T, Kim JJ, Hwang E, Ryu KS, Cheong HK, Cheong C, Ko JS, Enomoto T, Karplus PA, Güntert P, Tada S, Jeon YH, Cho Y. Structure of the Cdt1 C-terminal domain: conservation of the winged helix fold in replication licensing factors. Protein Sci 2010; 18:2252-64. [PMID: 19722278 DOI: 10.1002/pro.236] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
In eukaryotic replication licensing, Cdt1 plays a key role by recruiting the MCM2-7 complex onto the origin of chromosome. The C-terminal domain of mouse Cdt1 (mCdt1C), the most conserved region in Cdt1, is essential for licensing and directly interacts with the MCM2-7 complex. We have determined the structures of mCdt1CS (mCdt1C_small; residues 452 to 557) and mCdt1CL (mCdt1C_large; residues 420 to 557) using X-ray crystallography and solution NMR spectroscopy, respectively. While the N-terminal 31 residues of mCdt1CL form a flexible loop with a short helix near the middle, the rest of mCdt1C folds into a winged helix structure. Together with the middle domain of mouse Cdt1 (mCdt1M, residues 172-368), this study reveals that Cdt1 is formed with a tandem repeat of the winged helix domain. The winged helix fold is also conserved in other licensing factors including archaeal ORC and Cdc6, which supports an idea that these replication initiators may have evolved from a common ancestor. Based on the structure of mCdt1C, in conjunction with the biochemical analysis, we propose a binding site for the MCM complex within the mCdt1C.
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Affiliation(s)
- Bulat I Khayrutdinov
- The Magnetic Resonance Team, Korea Basic Science Institute, 804-1 Yangchung-Ri, Ochang, Chungbuk 363-883, South Korea
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23
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De Marco V, Gillespie PJ, Li A, Karantzelis N, Christodoulou E, Klompmaker R, van Gerwen S, Fish A, Petoukhov MV, Iliou MS, Lygerou Z, Medema RH, Blow JJ, Svergun DI, Taraviras S, Perrakis A. Quaternary structure of the human Cdt1-Geminin complex regulates DNA replication licensing. Proc Natl Acad Sci U S A 2009; 106:19807-12. [PMID: 19906994 PMCID: PMC2775996 DOI: 10.1073/pnas.0905281106] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2009] [Indexed: 01/12/2023] Open
Abstract
All organisms need to ensure that no DNA segments are rereplicated in a single cell cycle. Eukaryotes achieve this through a process called origin licensing, which involves tight spatiotemporal control of the assembly of prereplicative complexes (pre-RCs) onto chromatin. Cdt1 is a key component and crucial regulator of pre-RC assembly. In higher eukaryotes, timely inhibition of Cdt1 by Geminin is essential to prevent DNA rereplication. Here, we address the mechanism of DNA licensing inhibition by Geminin, by combining X-ray crystallography, small-angle X-ray scattering, and functional studies in Xenopus and mammalian cells. Our findings show that the Cdt1:Geminin complex can exist in two distinct forms, a "permissive" heterotrimer and an "inhibitory" heterohexamer. Specific Cdt1 residues, buried in the heterohexamer, are important for licensing. We postulate that the transition between the heterotrimer and the heterohexamer represents a molecular switch between licensing-competent and licensing-defective states.
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Affiliation(s)
- V. De Marco
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - P. J. Gillespie
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - A. Li
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | | | - E. Christodoulou
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - R. Klompmaker
- Department of Medical Oncology and Cancer Genomics Center, Laboratory of Experimental Oncology, University Medical Center Utrecht, Universiteitsweg 100, 3584CG Utrecht, The Netherlands; and
| | - S. van Gerwen
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - A. Fish
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - M. V. Petoukhov
- European Molecular Biology Laboratory, Hamburg Outstation, Notkestrasse 85, D-22603 Hamburg, Germany
| | - M. S. Iliou
- Biology, Medical School, University of Patras, 26500 Rio, Patras, Greece
| | - Z. Lygerou
- Biology, Medical School, University of Patras, 26500 Rio, Patras, Greece
| | - R. H. Medema
- Department of Medical Oncology and Cancer Genomics Center, Laboratory of Experimental Oncology, University Medical Center Utrecht, Universiteitsweg 100, 3584CG Utrecht, The Netherlands; and
| | - J. J. Blow
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - D. I. Svergun
- European Molecular Biology Laboratory, Hamburg Outstation, Notkestrasse 85, D-22603 Hamburg, Germany
| | | | - A. Perrakis
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
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24
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Kisielewska J, Philipova R, Huang JY, Whitaker M. MAP kinase dependent cyclinE/cdk2 activity promotes DNA replication in early sea urchin embryos. Dev Biol 2009; 334:383-94. [PMID: 19665013 PMCID: PMC2789238 DOI: 10.1016/j.ydbio.2009.07.043] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2009] [Revised: 06/30/2009] [Accepted: 07/27/2009] [Indexed: 12/23/2022]
Abstract
Sea urchins provide an excellent model for studying cell cycle control mechanisms governing DNA replication in vivo. Fertilization and cell cycle progression are tightly coordinated by Ca(2+) signals, but the mechanisms underlying the onset of DNA replication after fertilization remain less clear. In this study we demonstrate that calcium-dependent activation of ERK1 promotes accumulation of cyclinE/cdk2 into the male and female pronucleus and entry into first S-phase. We show that cdk2 activity rises quickly after fertilization to a maximum at 4 min, corresponding in timing to the early ERK1 activity peak. Abolishing MAP kinase activity after fertilization with MEK inhibitor, U0126, substantially reduces the early peak of cdk2 activity and prevents cyclinE and cdk2 accumulation in both sperm pronucleus and zygote nucleus in vivo. Both p27(kip1) and roscovitine, cdk2 inhibitors, prevented DNA replication suggesting cdk2 involvement in this process in sea urchin. Inhibition of cdk2 activity using p27(kip1) had no effect on the phosphorylation of MBP by ERK, but completely abolished phosphorylation of retinoblastoma protein, a cdk2 substrate, indicating that cdk2 activity is downstream of ERK1 activation. This pattern of regulation of DNA synthesis conforms to the pattern observed in mammalian somatic cells.
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Affiliation(s)
| | | | | | - M. Whitaker
- The Institute for Cell and Molecular Biosciences, Medical School, Faculty of Medical Sciences, Newcastle University, Framlington Place, NE2 4HH, Newcastle upon Tyne, UK
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25
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Narasimhachar Y, Coué M. Geminin stabilizes Cdt1 during meiosis in Xenopus oocytes. J Biol Chem 2009; 284:27235-42. [PMID: 19656945 DOI: 10.1074/jbc.m109.008854] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
During the mitotic cell cycle, Geminin can act both as a promoter and inhibitor of initiation of DNA replication. As a promoter, Geminin stabilizes Cdt1 and facilitates its accumulation leading to the assembly of the pre-replication complex on DNA. As an inhibitor, Geminin prevents Cdt1 from loading the mini-chromosome maintenance complex onto pre-replication complexes in late S, G(2), and M phases. Here we show that during meiosis Geminin functions as a stabilizer of Cdt1 promoting its accumulation for the early division cycles of the embryo. Depletion of Geminin in Xenopus immature oocytes leads to a decrease of Cdt1 protein levels during maturation and after activation of these oocytes. Injection of exogenous recombinant Geminin into the depleted oocytes rescues Cdt1 levels demonstrating that Geminin stabilizes Cdt1 during meiosis and after fertilization. Furthermore, Geminin-depleted oocytes did not replicate their DNA after meiosis I indicating that Geminin does not act as an inhibitor of initiation of DNA replication between meiosis I and meiosis II.
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Affiliation(s)
- Yadushyla Narasimhachar
- Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
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26
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Liu X, Huang S, Ma J, Li C, Zhang Y, Luo L. NF-kappaB and Snail1a coordinate the cell cycle with gastrulation. ACTA ACUST UNITED AC 2009; 184:805-15. [PMID: 19307597 PMCID: PMC2699144 DOI: 10.1083/jcb.200806074] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The cell cycle needs to strictly coordinate with developmental processes to ensure correct generation of the body plan and different tissues. However, the molecular mechanism underlying the coordination remains largely unknown. In this study, we investigate how the cell cycle coordinates gastrulation cell movements in zebrafish. We present a system to modulate the cell cycle in early zebrafish embryos by manipulating the geminin-Cdt1 balance. Alterations of the cell cycle change the apoptotic level during gastrulation, which correlates with the nuclear level of antiapoptotic nuclear factor κB (NF-κB). NF-κB associates with the Snail1a promoter region on the chromatin and directly activates Snail1a, an important factor controlling cell delamination, which is the initial step of mesendodermal cell movements during gastrulation. In effect, the cell cycle coordinates the delamination of mesendodermal cells through the transcription of Snail1a. Our results suggest a molecular mechanism by which NF-κB and Snail1a coordinate the cell cycle through gastrulation.
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Affiliation(s)
- Xiaolin Liu
- Key Laboratory of Aquatic Organism Reproduction and Development, Ministry of Education, Key Laboratory of Aquatic Science of Chongqing, School of Life Science, Southwest University, Beibei, Chongqing, China
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27
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Tsuyama T, Watanabe S, Aoki A, Cho Y, Seki M, Enomoto T, Tada S. Repression of nascent strand elongation by deregulated Cdt1 during DNA replication in Xenopus egg extracts. Mol Biol Cell 2008; 20:937-47. [PMID: 19064889 DOI: 10.1091/mbc.e08-06-0613] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Excess Cdt1 reportedly induces rereplication of chromatin in cultured cells and Xenopus egg extracts, suggesting that the regulation of Cdt1 activity by cell cycle-dependent proteolysis and expression of the Cdt1 inhibitor geminin is crucial for the inhibition of chromosomal overreplication between S phase and metaphase. We analyzed the consequences of excess Cdt1 for DNA replication and found that increased Cdt1 activity inhibited the elongation of nascent strands in Xenopus egg extracts. In Cdt1-supplemented extracts, overreplication was remarkably induced by the further addition of the Cdt1-binding domain of geminin (Gem79-130), which lacks licensing inhibitor activity. Further analyses indicated that fully active geminin, as well as Gem79-130, restored nascent strand elongation in Cdt1-supplemented extracts even after the Cdt1-induced stalling of replication fork elongation had been established. Our results demonstrate an unforeseen, negative role for Cdt1 in elongation and suggest that its function in the control of replication should be redefined. We propose a novel surveillance mechanism in which Cdt1 blocks nascent chain elongation after detecting illegitimate activation of the licensing system.
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Affiliation(s)
- Takashi Tsuyama
- Molecular Cell Biology Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Miyagi, 980-8578, Japan
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28
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Abstract
Correct regulation of the replication licensing system ensures that chromosomal DNA is precisely duplicated in each cell division cycle. Licensing proteins are inappropriately expressed at an early stage of tumorigenesis in a wide variety of cancers. Here we discuss evidence that misregulation of replication licensing is a consequence of oncogene-induced cell proliferation. This misregulation can cause either under- or over-replication of chromosomal DNA, and could explain the genetic instability commonly seen in cancer cells.
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Affiliation(s)
- J Julian Blow
- Wellcome Trust Centre for Gene Regulation & Expression, University of Dundee, DD1 5EH, UK.
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29
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van Leuken R, Clijsters L, Wolthuis R. To cell cycle, swing the APC/C. Biochim Biophys Acta Rev Cancer 2008; 1786:49-59. [DOI: 10.1016/j.bbcan.2008.05.002] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2008] [Revised: 05/05/2008] [Accepted: 05/13/2008] [Indexed: 11/30/2022]
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30
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Polycomb-group complex 1 acts as an E3 ubiquitin ligase for Geminin to sustain hematopoietic stem cell activity. Proc Natl Acad Sci U S A 2008; 105:10396-401. [PMID: 18650381 DOI: 10.1073/pnas.0800672105] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Polycomb-group (PcG) genes encode multimeric nuclear protein complexes, PcG complex 1 and 2. PcG complex 2 was proved to induce transcription repression and to further methylate histone H3 at lysine-27 (H3K27). Subsequently PcG complex 1 is recruited through recognition of methylated H3K27 and maintains the transcription silencing by mediating monoubiquitination of histone H2A at lysine-119. Genetic evidence demonstrated a crucial role for PcG complex 1 in stem cells, and Bmi1, a member of PcG complex 1, was shown to sustain adult stem cells through direct repression of the INK4a locus encoding cyclin-dependent kinase inhibitor, p16CKI, and p19ARF. The molecular functions of PcG complex 1, however, remain insufficiently understood. In our study, deficiency of Rae28, a member of PcG complex 1, was found to impair ubiquitin-proteasome-mediated degradation of Geminin, an inhibitor of DNA replication licensing factor Cdt1, and to increase protein stability. The resultant accumulation of Geminin, based on evidence from retroviral transduction experiments, presumably eliminated hematopoietic stem cell activity in Rae28-deficient mice. Rae28 mediates recruiting Scmh1, which provides PcG complex 1 an interaction domain for Geminin. Moreover, PcG complex 1 acts as the E3 ubiquitin ligase for Geminin, as we demonstrated in vivo as well as in vitro by using purified recombinant PcG complex 1 reconstituted in insect cells. Our findings suggest that PcG complex 1 supports the activity of hematopoietic stem cells, in which high-level Geminin expression induces quiescence securing genome stability, by enhancing cycling capability and hematopoietic activity through direct regulation of Geminin.
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31
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Gillespie PJ, Khoudoli GA, Stewart G, Swedlow JR, Blow J. ELYS/MEL-28 chromatin association coordinates nuclear pore complex assembly and replication licensing. Curr Biol 2007; 17:1657-62. [PMID: 17825564 PMCID: PMC2267255 DOI: 10.1016/j.cub.2007.08.041] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2007] [Revised: 07/27/2007] [Accepted: 08/10/2007] [Indexed: 10/30/2022]
Abstract
Xenopus egg extract supports all the major cell-cycle transitions in vitro. We have used a proteomics approach to identify proteins whose abundance on chromatin changes during the course of an in vitro cell cycle. One of the proteins we identified was ELYS/MEL-28, which has recently been described as the earliest-acting factor known to be required for nuclear pore complex (NPC) assembly [1-4]. ELYS interacts with the Nup107-160 complex and is required for its association with chromatin. ELYS contains an AT-hook domain, which we show binds to chromatin with a high affinity. This domain can compete with full-length ELYS for chromatin association, thereby blocking NPC assembly. This provides evidence that ELYS interacts directly with chromatin and that this interaction is essential for NPC assembly and compartmentalization of chromosomal DNA within the cell. Furthermore, we detected a physical association on chromatin between ELYS and the Mcm2-7 replication-licensing proteins. ELYS chromatin loading, NPC assembly, and nuclear growth were delayed when Mcm2-7 was prevented from loading onto chromatin. Because nuclear assembly is required to shut down licensing prior to entry into S phase, our results suggest a mechanism by which these two early cell-cycle events are coordinated with one another.
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Affiliation(s)
- Peter J. Gillespie
- Division of Gene Regulation and Expression, College of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Guennadi A. Khoudoli
- Division of Gene Regulation and Expression, College of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Graeme Stewart
- Division of Gene Regulation and Expression, College of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Jason R. Swedlow
- Division of Gene Regulation and Expression, College of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - J. Julian Blow
- Division of Gene Regulation and Expression, College of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
- Corresponding author
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32
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Luo L, Uerlings Y, Happel N, Asli NS, Knoetgen H, Kessel M. Regulation of geminin functions by cell cycle-dependent nuclear-cytoplasmic shuttling. Mol Cell Biol 2007; 27:4737-44. [PMID: 17470552 PMCID: PMC1951490 DOI: 10.1128/mcb.00123-07] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2007] [Revised: 02/27/2007] [Accepted: 04/18/2007] [Indexed: 12/24/2022] Open
Abstract
The geminin protein functions both as a DNA rereplication inhibitor through association with Cdt1 and as a repressor of Hox gene transcription through the polycomb pathway. Here, we report that the functions of avian geminin are coordinated with and regulated by cell cycle-dependent nuclear-cytoplasmic shuttling. In S phase, geminin enters nuclei and inhibits both loading of the minichromosome maintenance (MCM) complex onto chromatin and Hox gene transcription. At the end of mitosis, geminin is exported from nuclei by the exportin protein Crm1 and is unavailable in the nucleus during the next G(1) phase, thus ensuring proper chromatin loading of the MCM complex and Hox gene transcription. This mechanism for regulating the functions of geminin adds to distinct mechanisms, such as protein degradation and ubiquitination, applied in other vertebrates.
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Affiliation(s)
- Lingfei Luo
- Department of Molecular Cell Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
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33
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Arias EE, Walter JC. Strength in numbers: preventing rereplication via multiple mechanisms in eukaryotic cells. Genes Dev 2007; 21:497-518. [PMID: 17344412 DOI: 10.1101/gad.1508907] [Citation(s) in RCA: 313] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
In eukaryotic cells, prereplication complexes (pre-RCs) are assembled on chromatin in the G1 phase, rendering origins of DNA replication competent to initiate DNA synthesis. When DNA replication commences in S phase, pre-RCs are disassembled, and multiple initiations from the same origin do not occur because new rounds of pre-RC assembly are inhibited. In most experimental organisms, multiple mechanisms that prevent pre-RC assembly have now been identified, and rereplication within the same cell cycle can be induced through defined perturbations of these mechanisms. This review summarizes the diverse array of inhibitory pathways used by different organisms to prevent pre-RC assembly, and focuses on the challenge of understanding how in any one cell type, various mechanisms cooperate to strictly enforce once per cell cycle regulation of DNA replication.
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Affiliation(s)
- Emily E Arias
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
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Roukos V, Iliou MS, Nishitani H, Gentzel M, Wilm M, Taraviras S, Lygerou Z. Geminin cleavage during apoptosis by caspase-3 alters its binding ability to the SWI/SNF subunit Brahma. J Biol Chem 2007; 282:9346-9357. [PMID: 17261582 DOI: 10.1074/jbc.m611643200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Geminin has been proposed to coordinate cell cycle and differentiation events through balanced interactions with the cell cycle regulator Cdt1 and with homeobox transcription factors and chromatin remodeling activities implicated in cell fate decisions. Here we show that Geminin is cleaved in primary cells and cancer cell lines induced to undergo apoptosis by a variety of stimuli. Geminin targeting is mediated by caspase-3 both in vivo and in vitro. Two sites at the carboxyl terminus of Geminin (named C1 and C2) are cleaved by the caspase, producing truncated forms of Geminin. We provide evidence that Geminin cleavage is regulated by phosphorylation. Casein kinase II alters Geminin cleavage at site C1 in vitro, whereas mutating phosphorylation competent Ser/Thr residues proximal to site C1 affects Geminin cleavage in vivo. We show that truncated Geminin produced by cleavage at C1 can promote apoptosis. In contrast, Geminin cleaved at site C2 has lost the ability to interact with Brahma (Brm), a catalytic subunit of the SWI/SNF chromatin remodeling complex, while binding efficiently to Cdt1, indicating that targeting of Geminin during apoptosis differentially affects interactions with its binding partners.
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Affiliation(s)
- Vassilis Roukos
- Laboratory of General Biology, School of Medicine, University of Patras, 26500 Rio, Patras, Greece
| | - Maria S Iliou
- Laboratory of General Biology, School of Medicine, University of Patras, 26500 Rio, Patras, Greece
| | - Hideo Nishitani
- Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Higashi-ku, Fukuoka 812-8582, Japan
| | - Marc Gentzel
- Gene Expression Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
| | - Matthias Wilm
- Gene Expression Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
| | - Stavros Taraviras
- Laboratory of Pharmacology, Medical School, University of Patras, 26500 Rio, Patras, Greece
| | - Zoi Lygerou
- Laboratory of General Biology, School of Medicine, University of Patras, 26500 Rio, Patras, Greece.
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35
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Davidson IF, Li A, Blow JJ. Deregulated replication licensing causes DNA fragmentation consistent with head-to-tail fork collision. Mol Cell 2006; 24:433-43. [PMID: 17081992 PMCID: PMC1819398 DOI: 10.1016/j.molcel.2006.09.010] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2006] [Revised: 08/07/2006] [Accepted: 09/18/2006] [Indexed: 12/29/2022]
Abstract
Correct regulation of the replication licensing system ensures that no DNA is rereplicated in a single cell cycle. When the licensing protein Cdt1 is overexpressed in G2 phase of the cell cycle, replication origins are relicensed and the DNA is rereplicated. At the same time, checkpoint pathways are activated that block further cell cycle progression. We have studied the consequence of deregulating the licensing system by adding recombinant Cdt1 to Xenopus egg extracts. We show that Cdt1 induces checkpoint activation and the appearance of small fragments of double-stranded DNA. DNA fragmentation and strong checkpoint activation are dependent on uncontrolled rereplication and do not occur after a single coordinated round of rereplication. The DNA fragments are composed exclusively of rereplicated DNA. The unusual characteristics of these fragments suggest that they result from head-to-tail collision (rear ending) of replication forks chasing one another along the same DNA template.
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Affiliation(s)
- Iain F. Davidson
- School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Anatoliy Li
- School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - J. Julian Blow
- School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
- Corresponding author
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36
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Fujita M. Cdt1 revisited: complex and tight regulation during the cell cycle and consequences of deregulation in mammalian cells. Cell Div 2006; 1:22. [PMID: 17042960 PMCID: PMC1621056 DOI: 10.1186/1747-1028-1-22] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2006] [Accepted: 10/17/2006] [Indexed: 12/31/2022] Open
Abstract
In eukaryotic cells, replication of genomic DNA initiates from multiple replication origins distributed on multiple chromosomes. To ensure that each origin is activated precisely only once during each S phase, a system has evolved which features periodic assembly and disassembly of essential pre-replication complexes (pre-RCs) at replication origins. The pre-RC assembly reaction involves the loading of a presumptive replicative helicase, the MCM2-7 complexes, onto chromatin by the origin recognition complex (ORC) and two essential factors, CDC6 and Cdt1. The eukaryotic cell cycle is driven by the periodic activation and inactivation of cyclin-dependent kinases (Cdks) and assembly of pre-RCs can only occur during the low Cdk activity period from late mitosis through G1 phase, with inappropriate re-assembly suppressed during S, G2, and M phases. It was originally suggested that inhibition of Cdt1 function after S phase in vertebrate cells is due to geminin binding and that Cdt1 hyperfunction resulting from Cdt1-geminin imbalance induces re-replication. However, recent progress has revealed that Cdt1 activity is more strictly regulated by two other mechanisms in addition to geminin: (1) functional and SCFSkp2-mediated proteolytic regulation through phosphorylation by Cdks; and (2) replication-coupled proteolysis mediated by the Cullin4-DDB1Cdt2 ubiquitin ligase and PCNA, an eukaryotic sliding clamp stimulating replicative DNA polymerases. The tight regulation implies that Cdt1 control is especially critical for the regulation of DNA replication in mammalian cells. Indeed, Cdt1 overexpression evokes chromosomal damage even without re-replication. Furthermore, deregulated Cdt1 induces chromosomal instability in normal human cells. Since Cdt1 is overexpressed in cancer cells, this could be a new molecular mechanism leading to carcinogenesis. In this review, recent insights into Cdt1 function and regulation in mammalian cells are discussed.
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Affiliation(s)
- Masatoshi Fujita
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan.
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37
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Das-Bradoo S, Ricke RM, Bielinsky AK. Interaction between PCNA and diubiquitinated Mcm10 is essential for cell growth in budding yeast. Mol Cell Biol 2006; 26:4806-17. [PMID: 16782870 PMCID: PMC1489165 DOI: 10.1128/mcb.02062-05] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The minichromosome maintenance protein 10 (Mcm10) is an evolutionarily conserved factor that is essential for replication initiation and elongation. Mcm10 is part of the eukaryotic replication fork and interacts with a variety of proteins, including the Mcm2-7 helicase and DNA polymerase alpha/primase complexes. A motif search revealed a match to the proliferating cell nuclear antigen (PCNA)-interacting protein (PIP) box in Mcm10. Here, we demonstrate a direct interaction between Mcm10 and PCNA that is alleviated by mutations in conserved residues of the PIP box. Interestingly, only the diubiquitinated form of Mcm10 binds to PCNA. Diubiquitination of Mcm10 is cell cycle regulated; it first appears in late G(1) and persists throughout S phase. During this time, diubiquitinated Mcm10 is associated with chromatin, suggesting a direct role in DNA replication. Surprisingly, a Y245A substitution in the PIP box of Mcm10 that inhibits the interaction with PCNA abolishes cell proliferation. This severe-growth phenotype, which has not been observed for analogous mutations in other PCNA-interacting proteins, is rescued by a compensatory mutation in PCNA that restores interaction with Mcm10-Y245A. Taken together, our results suggest that diubiquitinated Mcm10 interacts with PCNA to facilitate an essential step in DNA elongation.
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Affiliation(s)
- Sapna Das-Bradoo
- University of Minnesota, Biochemistry, Molecular Biology and Biophysics, 321 Church Street SE, 6-155 Jackson Hall, Minneapolis, MN 55455, USA
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38
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DePamphilis ML, Blow JJ, Ghosh S, Saha T, Noguchi K, Vassilev A. Regulating the licensing of DNA replication origins in metazoa. Curr Opin Cell Biol 2006; 18:231-9. [PMID: 16650748 DOI: 10.1016/j.ceb.2006.04.001] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2006] [Accepted: 04/04/2006] [Indexed: 01/19/2023]
Abstract
Eukaryotic DNA replication is a highly conserved process; the proteins and sequence of events that replicate animal genomes are remarkably similar to those that replicate yeast genomes. Moreover, the assembly of prereplication complexes at DNA replication origins ('DNA licensing') is regulated in all eukaryotes so that no origin fires more than once in a single cell cycle. And yet there are significant differences between species both in the selection of replication origins and in the way in which these origins are licensed to operate. Moreover, these differences impart advantages to multicellular animals and plants that facilitate their development, such as better control over endoreduplication, flexibility in origin selection, and discrimination between quiescent and proliferative states.
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Affiliation(s)
- Melvin L DePamphilis
- National Institute of Child Health and Human Development, National Institutes of Health, Building 6/3A-15, 9000 Rockville Pike, Bethesda, MD 20892-2753, USA.
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39
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Iizuka M, Matsui T, Takisawa H, Smith MM. Regulation of replication licensing by acetyltransferase Hbo1. Mol Cell Biol 2006; 26:1098-108. [PMID: 16428461 PMCID: PMC1347032 DOI: 10.1128/mcb.26.3.1098-1108.2006] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The initiation of DNA replication is tightly regulated in eukaryotic cells to ensure that the genome is precisely duplicated once and only once per cell cycle. This is accomplished by controlling the assembly of a prereplicative complex (pre-RC) which involves the sequential binding to replication origins of the origin recognition complex (ORC), Cdc6/Cdc18, Cdt1, and the minichromosome maintenance complex (Mcm2-Mcm7, or Mcm2-7). Several mechanisms of pre-RC regulation are known, including ATP utilization, cyclin-dependent kinase levels, protein turnover, and Cdt1 binding by geminin. Histone acetylation may also affect the initiation of DNA replication, but at present neither the enzymes nor the steps involved are known. Here, we show that Hbo1, a member of the MYST histone acetyltransferase family, is a previously unrecognized positive regulatory factor for pre-RC assembly. When Hbo1 expression was inhibited in human cells, Mcm2-7 failed to associate with chromatin even though ORC and Cdc6 loading was normal. When Xenopus egg extracts were immunodepleted of Xenopus Hbo1 (XHbo1), chromatin binding of Mcm2-7 was lost, and DNA replication was abolished. The binding of Mcm2-7 to chromatin in XHbo1-depleted extracts could be restored by the addition of recombinant Cdt1.
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Affiliation(s)
- Masayoshi Iizuka
- Department of Microbiology, University of Virginia Health System, P.O. Box 800734, Charlottesville, VA 22908-0734, USA
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40
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Zhu W, Abbas T, Dutta A. DNA replication and genomic instability. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2006; 570:249-79. [PMID: 18727504 DOI: 10.1007/1-4020-3764-3_9] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Wenge Zhu
- Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
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41
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Pines J. Mitosis: a matter of getting rid of the right protein at the right time. Trends Cell Biol 2005; 16:55-63. [PMID: 16337124 DOI: 10.1016/j.tcb.2005.11.006] [Citation(s) in RCA: 202] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2005] [Revised: 10/04/2005] [Accepted: 11/21/2005] [Indexed: 01/08/2023]
Abstract
There are two major problems for the cell to solve in mitosis: how to ensure that each daughter cell receives an equal and identical complement of the genome, and how to prevent cell separation before chromosome segregation. Both these problems are solved by controlling when two specific proteins are destroyed: securin, an inhibitor of chromosome segregation, and cyclin B, which inhibits cell separation (cytokinesis). It has recently become clear that several other proteins are degraded at specific points in mitosis. This review (which is part of the Chromosome Segregation and Aneuploidy series) focuses on how specific proteins are selected for proteolysis at defined points in mitosis and how this contributes to the proper coordination of chromosome segregation and cytokinesis.
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Affiliation(s)
- Jonathon Pines
- Wellcome/Cancer Research UK Gurdon Institute & Dept of Zoology, Tennis Court Road, Cambridge, UK CB2 1QN.
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42
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Abstract
To ensure its duplication, chromosomal DNA must be precisely duplicated in each cell cycle, with no sections left unreplicated, and no sections replicated more than once. Eukaryotic cells achieve this by dividing replication into two non-overlapping phases. During late mitosis and G1, replication origins are 'licensed' for replication by loading the minichromosome maintenance (Mcm) 2-7 proteins to form a pre-replicative complex. Mcm2-7 proteins are then essential for initiating and elongating replication forks during S phase. Recent data have provided biochemical and structural insight into the process of replication licensing and the mechanisms that regulate it during the cell cycle.
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Affiliation(s)
- J Julian Blow
- Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, UK.
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43
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Abstract
Initiation and completion of DNA replication defines the beginning and ending of S phase of the cell cycle. Successful progression through S phase requires that replication be properly regulated and monitored to ensure that the entire genome is duplicated exactly once, without errors, in a timely fashion. Given the immense size and complexity of eukaryotic genomes, this presents a significant challenge for the cell. As a result, DNA replication has evolved into a tightly regulated process involving the coordinated action of numerous factors that function in all phases of the cell cycle. We will review our current understanding of these processes from the formation of prereplicative complexes in preparation for S phase to the series of events that culminate in the loading of DNA polymerases during S phase. We will incorporate structural data from archaeal and bacterial replication proteins and discuss their implications for understanding the mechanism of action of their corresponding eukaryotic homologues. We will also describe the concept of replication licensing which protects against genomic instability by limiting initiation events to once per cell cycle. Lastly, we will review our knowledge of checkpoint pathways that maintain the integrity of stalled forks and relay defects in replication to the rest of the cell cycle.
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Affiliation(s)
- David Y Takeda
- Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA
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44
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Saxena S, Dutta A. Geminin-Cdt1 balance is critical for genetic stability. Mutat Res 2005; 569:111-21. [PMID: 15603756 DOI: 10.1016/j.mrfmmm.2004.05.026] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2004] [Accepted: 05/04/2004] [Indexed: 01/14/2023]
Abstract
A cell limits its DNA replication activity to once per cell division cycle to maintain its genomic integrity. Studies in a variety of organisms are elucidating how these controls are exercised. Key amongst these is the regulation of replication initiator proteins such as Cdt1. Cdt1 is present in cells in G1 phase where it is required for initiation of replication. Once origins have fired, Cdt1 is either exported out of the nucleus or degraded, thereby preventing another round of replication. Higher eukaryotes have evolved another redundant mechanism, an inhibitor called geminin, to restrain Cdt1 activity. Studies in multiple organisms have shown that unregulated Cdt1 activity stimulates overreplication of the genome. Interestingly, the same seems to be true when geminin is depleted. The imbalance in the activities of these proteins causes the activation of key checkpoint proteins, the ATM/ATR kinases and the tumor suppressor, p53. This review proposes that a balance between Cdt1 and geminin is important for maintaining genomic stability.
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Affiliation(s)
- Sandeep Saxena
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908, USA
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45
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Abstract
Eukaryotic genomes are replicated from large numbers of replication origins distributed on multiple chromosomes. The activity of these origins must be coordinated so that the entire genome is efficiently and accurately replicated yet no region of the genome is ever replicated more than once. The past decade has seen significant advances in understanding how the initiation of DNA replication is regulated by key cell-cycle regulators, including the cyclin dependent kinases (CDKs) and the anaphase promoting complex/cyclosome (APC/C). The assembly of essential prereplicative complexes (pre-RCs) at origins only occurs when CDK activity is low and APC/C activity is high. Origin firing, however, can only occur when the APC/C is inactivated and CDKs become active. This two step mechanism ensures that no origin can fire more than once in a cell cycle. In all eukaryotes tested, CDKs can contribute to the inhibition of pre-RC assembly. This inhibition is characterised both by high degrees of redundancy and evolutionary plasticity. Geminin plays a crucial role in inhibiting licensing in metazoans and, like cyclins, is inactivated by the APC/C. Strategies involved in preventing re-replication in different organisms will be discussed.
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Affiliation(s)
- John F X Diffley
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Hertfordshire EN6 3LD, UK.
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46
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Tsuyama T, Tada S, Watanabe S, Seki M, Enomoto T. Licensing for DNA replication requires a strict sequential assembly of Cdc6 and Cdt1 onto chromatin in Xenopus egg extracts. Nucleic Acids Res 2005; 33:765-75. [PMID: 15687385 PMCID: PMC548366 DOI: 10.1093/nar/gki226] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Replication origins are licensed for a single initiation event by the loading of Mcm2-7 proteins during late mitosis and G1. Sequential associations of origin recognition complex, Cdc6 and Mcm2-7 are essential for completion of the licensing. Although Cdt1 also binds to the chromatin when the licensing reaction takes place, whether the binding is a requirement for Cdt1 to function is unclear. To analyze the relevance of the chromatin association of Cdt1, we carried out chromatin transfer experiments using either immunodepleted Xenopus egg extracts or purified proteins. Licensing assay and immunoblotting analyses indicated that Cdt1 could only license DNA replication and load Mcm2-7 onto DNA when it binds to chromatin that has already associated with Cdc6. These results provide evidence supporting that Cdc6 and Cdt1 must bind to chromatin in a strict order for DNA licensing to occur.
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Affiliation(s)
| | - Shusuke Tada
- To whom correspondence should be addressed. Tel: +81 22 217 6876; Fax: +81 22 217 6873;
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47
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Ferenbach A, Li A, Brito-Martins M, Blow JJ. Functional domains of the Xenopus replication licensing factor Cdt1. Nucleic Acids Res 2005; 33:316-24. [PMID: 15653632 PMCID: PMC546161 DOI: 10.1093/nar/gki176] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2004] [Revised: 12/20/2004] [Accepted: 12/20/2004] [Indexed: 12/21/2022] Open
Abstract
During late mitosis and early G1, replication origins are licensed for subsequent replication by loading heterohexamers of the mini-chromosome maintenance proteins (Mcm2-7). To prevent re-replication of DNA, the licensing system is down-regulated at other cell cycle stages. A small protein called geminin plays an important role in this down-regulation by binding and inhibiting the Cdt1 component of the licensing system. We examine here the organization of Xenopus Cdt1, delimiting regions of Cdt1 required for licensing and regions required for geminin interaction. The C-terminal 377 residues of Cdt1 are required for licensing and the extreme C-terminus contains a domain that interacts with an Mcm(2,4,6,7) complex. Two regions of Cdt1 interact with geminin: one at the N-terminus, and one in the centre of the protein. Only the central region binds geminin tightly enough to successfully compete with full-length Cdt1 for geminin binding. This interaction requires a predicted coiled-coil domain that is conserved amongst metazoan Cdt1 homologues. Geminin forms a homodimer, with each dimer binding one molecule of Cdt1. Separation of the domains necessary for licensing activity from domains required for a strong interaction with geminin generated a construct, whose licensing activity was partially insensitive to geminin inhibition.
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Affiliation(s)
- Andrew Ferenbach
- Wellcome Trust Biocentre, University of Dundee Dow Street, Dundee DD1 5EH, UK
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48
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Li A, Blow JJ. Cdt1 downregulation by proteolysis and geminin inhibition prevents DNA re-replication in Xenopus. EMBO J 2004; 24:395-404. [PMID: 15616577 PMCID: PMC545810 DOI: 10.1038/sj.emboj.7600520] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2004] [Accepted: 11/23/2004] [Indexed: 01/04/2023] Open
Abstract
In late mitosis and G1, Mcm2-7 are assembled onto replication origins to 'license' them for initiation. At other cell cycle stages, licensing is inhibited, thus ensuring that origins fire only once per cell cycle. Three additional factors--the origin recognition complex, Cdc6 and Cdt1--are required for origin licensing. We examine here how licensing is regulated in Xenopus egg extracts. We show that Cdt1 is downregulated late in the cell cycle by two different mechanisms: proteolysis, which occurs in part due to the activity of the anaphase-promoting complex (APC/C), and inhibition by a protein called geminin. If both these regulatory mechanisms are abrogated, extracts undergo uncontrolled re-licensing and re-replication. The extent of re-replication is limited by checkpoint kinases that are activated as a consequence of re-replication itself. These results allow us to build a comprehensive model of how re-replication of DNA is prevented in Xenopus, with Cdt1 regulation being the key feature. The results also explain the original experiments that led to the proposal of a replication licensing factor.
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Affiliation(s)
- Anatoliy Li
- Wellcome Trust Biocentre, University of Dundee, Dundee, UK
| | - J Julian Blow
- Wellcome Trust Biocentre, University of Dundee, Dundee, UK
- Wellcome Trust Biocentre, University of Dundee, Dow Street, Dundee DD1 5EH, UK. Tel.: +44 1382 345797; Fax: +44 1382 348072; E-mail:
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49
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Arias EE, Walter JC. Replication-dependent destruction of Cdt1 limits DNA replication to a single round per cell cycle in Xenopus egg extracts. Genes Dev 2004; 19:114-26. [PMID: 15598982 PMCID: PMC540230 DOI: 10.1101/gad.1255805] [Citation(s) in RCA: 163] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In eukaryotes, prereplication complexes (pre-RCs) containing ORC, Cdc6, Cdt1, and MCM2-7 are assembled on chromatin in the G1 phase. In S phase, when DNA replication initiates, pre-RCs are disassembled, and new pre-RC assembly is restricted until the following G1 period. As a result, DNA replication is limited to a single round per cell cycle. One inhibitor of pre-RC assembly, geminin, was discovered in Xenopus, and it binds and inactivates Cdt1 in S phase. However, removal of geminin from Xenopus egg extracts is insufficient to cause rereplication, suggesting that other safeguards against rereplication exist. Here, we show that Cdt1 is completely degraded by ubiquitin-mediated proteolysis during the course of the first round of DNA replication in Xenopus egg extracts. Degradation depends on Cdk2/Cyclin E, Cdc45, RPA, and polymerase alpha, demonstrating a requirement for replication initiation. Cdt1 is ubiquitinated on chromatin, and this process also requires replication initiation. Once replication has initiated, Cdk2/Cyclin E is dispensable for Cdt1 degradation. When fresh Cdt1 is supplied after the first round of DNA replication, significant rereplication results, and rereplication is enhanced in the absence of geminin. Our results identify a replication-dependent proteolytic pathway that targets Cdt1 and that acts redundantly with geminin to inactivate Cdt1 in S phase.
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Affiliation(s)
- Emily E Arias
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
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50
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Lee C, Hong B, Choi JM, Kim Y, Watanabe S, Ishimi Y, Enomoto T, Tada S, Kim Y, Cho Y. Structural basis for inhibition of the replication licensing factor Cdt1 by geminin. Nature 2004; 430:913-7. [PMID: 15286659 DOI: 10.1038/nature02813] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2004] [Accepted: 07/05/2004] [Indexed: 11/08/2022]
Abstract
To maintain chromosome stability in eukaryotic cells, replication origins must be licensed by loading mini-chromosome maintenance (MCM2-7) complexes once and only once per cell cycle. This licensing control is achieved through the activities of geminin and cyclin-dependent kinases. Geminin binds tightly to Cdt1, an essential component of the replication licensing system, and prevents the inappropriate reinitiation of replication on an already fired origin. The inhibitory effect of geminin is thought to prevent the interaction between Cdt1 and the MCM helicase. Here we describe the crystal structure of the mouse geminin-Cdt1 complex using tGeminin (residues 79-157, truncated geminin) and tCdt1 (residues 172-368, truncated Cdt1). The amino-terminal region of a coiled-coil dimer of tGeminin interacts with both N-terminal and carboxy-terminal parts of tCdt1. The primary interface relies on the steric complementarity between the tGeminin dimer and the hydrophobic face of the two short N-terminal helices of tCdt1 and, in particular, Pro 181, Ala 182, Tyr 183, Phe 186 and Leu 189. The crystal structure, in conjunction with our biochemical data, indicates that the N-terminal region of tGeminin might be required to anchor tCdt1, and the C-terminal region of tGeminin prevents access of the MCM complex to tCdt1 through steric hindrance.
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Affiliation(s)
- Changwook Lee
- National Creative Research Center for Structural Biology and Department of Life Science, Pohang University of Science and Technology, Hyo-ja dong, San31, Pohang, KyungBook, South Korea
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